The invention relates to an apparatus for laser surgery and particularly to keratotomy of the cornea using a laser, particuarly a UV-laser.
It is known, e.g. form the article "Excimer-Laser Surgery of the Cornea" by Stephen L. Trokel, American Journal of Ophthalmology, 1983, vol. 96, pp. 710-715 that in particular, argon-fluoride-excimer lasers with a wavelength of 193 nm are suitable for performing operations on the cornea. The object of such operations is e.g. to eliminate abnormal cornea curvatures by applying a specific "incison pattern". The literature discloses lasers of other wavelengths, e.g. r.f. lasers, which are suitable for keratotomy.
It is also known from the scientific literature, that light of other wavelengths is also suitable for keratotomy of the cornea.
In the known apparatuses for the keratotomy of the cornea, such as are e.g. described in the above article, a mask is placed just in front of the eye undergoinging the operation and is irradiated with UV-laser light.
As a result of this construction, the known apparatuses suffer from a number of disadvantages.
The laser beam must illuminate the diaphragm in which is located the desired "incision pattern" in a flat manner. As the incision pattern only takes up a small part of the illuminated surface, only a small part of the laser power is actually available for the operation.
An object of the present invention is to provide an apparatus for laser surgery and particularly for operating on the cornea, in which a large part of the laser power is available for the operation.
This object is achieved by providing the following apparatus. According to this invention, in place of the mask in which is provided the complete desired incision pattern, a single slit is used, whose alignment with respect to the laser beam remains unchanged throughout the operation and which is only modified with respect to its length and width. Following is provided the slit is provided an optical rotary device, is provided which rotates the slit image position on the tissue, e.g. the cornea on which the operation is to take place. As the laser beam now only has to illuminate the slit, whose angular alignment remains unchanged and in which only the length and width change within certain limits, substantially the complete laser power is available for the operation. Admittedly in the case of a complicated incision pattern, the individual parts thereof, e.g. in the case of a star-shaped incision pattern the individual arms of the star have to be successively illuminated, but as for each illumination process, a larger beam power is available, and the operating time is shorter than with the known apparatus, in which the complete incision pattern has to be illuminated with high absorbtion and/or reflection losses in the diaphragm.
In an advantageous feature of other preferred embodiments of the invention, the optical rotary device can be a known rotary prism, such as a Dove prism or an Oxley prism. However, in a preferred embodiment of the invention it is particularly advantageous to use a rotary prism formed from two parts whose entrance face and exit face are at right angles to the optical axis and that includes three surfaces, which totally reflect the beam and whose surface normals form an angle of 67.5.degree. , 90.degree. , and 112.5.degree. with the optical axis. Further the prism includes two passage faces between the two parts through which the beam passes at right angles. In this embodiment of the prism, all the beam passage faces are at right angles to the optical path and the slit image is not interrupted by interfaces, boundary surfaces and the like.
Since particularly when operating on the cornea, the tissue undergoing the operation is not planar and is instead typically highly curved, it is particularly advantageous to use the inventive rotary device in conjunction with an optical device, which images the slit image with a high depth of field on the tissue undergoing the operation.
In an advantageous feature of other embodiments of the invention, it has suprisingly been found that such a device can be a simple telecentric arrangement of two positive optical elements between which is arranged the slit and which is to be projected on to the tissue undergoing the operation. The optical rotary device can also be arranged between two collecting optical elements, which form a telecentric arrangement, or alternatively can follow these two elements. The arrangement between the two positive optical elements has the advantage that a short, compact construction is obtained.
The inventive apparatus of all embodiments of the invention can at any time be integrated into an ophthalmic examination apparatus, such as an ophthalmoscope or a slit lamp device. In the case of integration into a slit lamp device, fitting can e.g. take place into the actual slit lamp, or into the microscope bracket, if the laser beam is to be projected by the microscope bracket on to the eye. Such an apparatus has been proposed for a neodymium-YAG laser, whilst apparatuses in which the reflecting takes place by slit lamps have already been proposed for argon lasers. This known beam guidance can also be used for apparatuses with excimer lasers or lasers of other wavelengths, such as r.f. lasers and in other embodiments of the invention it is particularly advantageous to construct all the deflectors as fused quartz prisms, because in the case thereof the reflection losses are much lower than in the case of coated reflecting surfaces.
It is also possible to integrate all embodiments of the invention, into an apparatus, such as is described in a commonly-owned patent application filed on the same date filed Jun. 29, 1985 in Germany, Pat. No. 35 23 342.7. In this apparatus, the slit lamp is not privoted and is instead merely linearly displaced, whilst the chin rest is also movable. In this apparatus, the number of reflecting surfaces required for reflecting in the laser beam is particularly small, so that a particularly large proportion of the laser power is available for the operation. The reduction of the number of mirros used for guiding the beam compensates for any losses due to the rotary prisms.
The inventive apparatus has the advantage that a much larger proportion of the laser power is available for the actual operation than was the case in the known apparatuses. The inventively provided illumination of a slit fixed with respect to its alignment is assisted by the fact that an excimer laser without beam-forming measures already has an elongated cross-section, so that a beam section shape, when illuminates the slit in a coinciding manner can be achieved with simple measures, e.g. with a telecentric arrangement or with cylindrical lenses. Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing.